Well, I thought this could be an interesting topic. I work in retail (Wal*Mart) and, although I don't technically work in Electronics, I pretty much take care of the video games (working in the Connection Center, I tend to have the free time to do this and the Electronics Department Manager doesn't mind, since it gives her free time as well). I thought I'd start a topic about what's selling well and see if anyone else here works retail and what y'all are seeing selling well.
Of course there's the big winners of Wii and PS3. We can't keep either in stock - when we rarely get them.
The 360 is selling, although slowly. I think we sell more PS2's than 360s.
Game Boys... dang. The Game Boy micros didn't sell very well for Black Friday - we've got a ton left... but GBASPs... wow. We pretty much sell *out* of the blue and pink ones when we get them in (rarely now). The black one has stayed in stock, but we had tons of those and we're starting to run low on 'em.
We get tons of calls about DSes (?). Apparently, most places are out of stock on them. We finally sold out of the Grey Phats and have a few blues left. The Pink and Black DSLite is impossible to get (selling out the day we get them in, pretty much) and the white DSLite is slowly depleting.
PSPs... heh.
Game Wise? Guitar Hero II is the big winner here. We sold about 40 copies of this thing in a week. At $80 a pop, that's pretty impressive. Had we not sold out, we could have sold a lot more.
Unfortunatly, Madden 07 sells well.
Cars and Over the Hedge are pretty good sellers.
No big PS3 winners. No big Wii winners either (except, of course, Zelda). There really doesn't seem to be any big 360 games either... even Gears of War has sold pretty crappy. I think I've sold one PSP game - so Madden 07 is the winner there.

On the DS/GBA front, Nintendogs is still selling well - in fact, Dalmations is the only one we've got left. All the Mario games are selling well, of course.
Strangly enough, we get a lot of people looking for original XBox controllers.